The sesamoid bones are maintained in position by the suspensory ligament proximally and by a number of sesamoidean ligaments distally. Due to the great stress placed on the fetlock during fast exercise, the insertion of some of these ligaments can tear, which can result in inflammation and pain in this region, known as sesamoiditis.

The clinical signs are similar to, but less severe than, those resulting from sesamoid fracture. Depending on the extent of the damage, there are varying degrees of lameness and swelling. Pain and heat are evident on palpation and flexion of the fetlock joint. The radiographic features include periosteal new bone proliferation or osteolytic lesions (or both), particularly on the abaxial surface of the affected sesamoid (enthesiophytosis of the suspensory ligament branch attachments). Radiolucent lines may be seen but must be distinguished from normal vascular channels running through the bone that are evident in young racehorses but rarely associated with pathology. Oblique radiographic views are essential for accurate diagnosis and evaluation.

The recommended treatment is a 2- to 3-wk course of phenylbutazone. For mild sesamoiditis, ≥6 mo rest is required; for severe cases, 9–12 mo. The insertion of the suspensory ligaments should be carefully evaluated by ultrasonography for concurrent lesions.